The present invention relates in general to semiconductor technology and in particular to improved Schottky rectifier structures and methods of manufacturing the same.
Silicon-based power rectifiers are well known and have been used in power electronic systems for many decades. Silicon Schottky rectifiers have generally been used in applications operating at mid to low voltages due to their lower on-state voltage drop and faster switching speed. A conventional planar Schottky rectifier structure is shown in FIG. 1A. A top metal electrode forms a Schottky contact with the underlying semiconductor region 106. The traditional method of optimizing this rectifier changes the Schottky contact metal to alter the barrier height. Although the on-state voltage drop can be reduced by decreasing the barrier height, the reverse leakage current increases exponentially leading to unstable operation at high temperatures. Attempts to improve upon this tradeoff between on-state and reverse blocking power losses has led to the development of the junction barrier controlled Schottky (JBS) structure shown in FIG. 1B.
In FIG. 1B, closely-spaced p-type regions 114 are formed in n-type region 112. A top metal electrode 113 forms a Schottky contact with the surface area of n-type region 112 between p-type regions 114, and forms an ohmic contact with p-type regions 114. The pn junction formed by p-type regions 114 and n-type region 112 forms a potential barrier below the Schottky contact, resulting in a lower electric field at the metal-semiconductor interface. The resulting suppression of the barrier height lowering responsible for the poor reverse leakage in these devices allowed some improvements in the power loss tradeoff. However, the Schottky contact area through which the on-state current flows is reduced due the lateral diffusion of p-type regions 114, and the series resistance is increased by current constriction between the junctions.
Further performance improvements have been obtained by the incorporation of a trench MOS region under the Schottky contact to create the trench MOS-barrier Schottky (TMBS) rectifier structure shown in FIG. 1C. The MOS structure greatly reduces the electric field under the Schottky contact while enabling the support of voltages far in excess of the parallel-plane breakdown voltage in mesa region 119. This allows optimizing mesa region 119 to have a higher diping concentration thus reducing the rectifier""s on state voltage drop A further improvement in the electric field distribution under the Schottky contact has been obtained by using a graded doping profile in the mesa region.
It has been observed however, that the TMBS structure suffers from high leakage due to phosphorous segregation at the oxide-silicon interface. The increased phosphorous concentration reduces the accumulation threshold on the mesa sidewalls and increases the leakage current. Further, the TMBS and JBS structures have higher capacitance due to the presence of MOS structures 118 in the TMBS structure and the presence of p-type regions 114 in the JBS structure.
Thus, Schottky rectifiers having a low forward voltage, high reverse breakdown voltage, and low capacitance which do not suffer from high leakage are desirable.
In accordance with an embodiment of the present invention, a semiconductor rectifier includes an insulation-filled trench formed in a semiconductor region. Strips of resistive material extend along the trench sidewalls. The strips of resistive material have a conductivity type opposite that of the semiconductor region. A conductor extends over and in contact with the semiconductor region so that the conductor and the underlying semiconductor region form a Schottky contact.
In one embodiment, the semiconductor region is formed over a substrate, and the substrate and the semiconductor region have the same conductivity type.
In another embodiment, the strips of resistive material are discontinuous along the bottom of the insulation-filled trench.
In another embodiment, the strips of resistive material comprise doped silicon material.
In another embodiment, the conductor is in contact with the strips of resistive material.
In another embodiment, the strips of resistive material comprise silicon material having a doping concentration of about four to five times greater than a doping concentration of the semiconductor region.
In accordance with another embodiment of the present invention, a semiconductor rectifier is formed as follows. A trench is formed in a semiconductor region. Strips of resistive material are formed along the trench sidewalls. The strips of resistive material have a conductivity type opposite that of the semiconductor region. The trench is substantially filled with insulating material. A conductor is formed over and in contact with the semiconductor region so that the conductor and the underlying semiconductor region form a Schottky contact.
In another embodiment, the semiconductor region is formed over a substrate, and the substrate and the semiconductor region have the same conductivity type.
In another embodiment, the strips of resistive material are discontinuous along the bottom of the trench.
In another embodiment, the strips of resistive material comprise silicon material having a doping concentration of about four to five times greater than a doping concentration of the semiconductor region.
The following detailed description and the accompanying drawings provide a better understanding of the nature and advantages of the present invention.